1. Field of the Invention
The present invention relates to aqueous binders based on polybutadiene which are suitable for use as air-drying coating materials and which can be processed entirely without organic solvents.
2. Description of the Background
Aqueous coating systems have become increasingly important as they enable reductions in solvent emissions.
As a consequence of the continual increase in environmental awareness, tighter statutory regulations and the introduction of so-called eco audits, the necessity of maintaining clean air continues. As a result, producers and users of coating systems must develop and employ processes and products devoid of harmful, environmentally polluting emissions.
Aqueous binders based on polybutadiene are obtainable by modification with maleic anhydride (MAA), wherein the resulting anhydride functions are reacted further to afford free carboxyl groups. Partial or complete neutralization of these carboxyl groups provides water-soluble or water-dispersible binders.
The known modification of polybutadienes with MAA is described, for example, in DE-B 12 92 299 and in DE-B 12 19 684. Films of such MAA adducts show improved substrate adhesion compared with those having polybutadienes which have not been modified.
Polybutadiene/maleic anhydride adducts can be partially esterified or amidated see DE 10 26 900. 25 07 809, 26 33 362 or 27 33 274. The monoesters or monoamides formed, respectively, in the reaction with alcohol or with secondary amines have free carboxyl groups. Some or all of these groups can be neutralized, thereby giving water-soluble or water-dispersible binders, respectively.
It is also possible to obtain water-soluble or water-dispersible binders by imidating the anhydride groups.
According to DE-A 25 53 593, water-dilutable polymer oil imides are obtained by reacting polybutadiene/maleic anhydride adducts with ammonia or urea.
In DE-A 27 54 733 or 26 16 591 maleic anhydride-containing polybutadienes are reacted with diamines which include one primary or one tertiary amine function. While the primary amine function undergoes an imidation reaction with the anhydride groups, the tertiary amine function can be neutralized with acids so that the polybutadienes thus functionalized likewise become soluble in water.
Polybutadiene oils having a high cis double bond content are advantageous as a base for paint binders because of the good drying properties in air and the outstanding chemical resistance of the paint films. An improvement in the drying properties, especially the initial physical drying of polybutadiene-based binders, can be achieved, according to DE-A 27 33 274, by a graft reaction with unsaturated monomers.
Grafted polybutadiene/maleic anhydride adducts of this kind can be made soluble or dispersible in water in the same way as described above: see DE 26 33 262, 27 33 274, 27 54 733 and EP 0 170 184.
Graft reactions of unsaturated monomers with polybutadiene/maleic anhydride adducts are carried out in solution or, preferably, as a bulk polymerization with free-radical initiators. Such free-radically controlled graft polymerizations generally proceed in an irregular and incomplete way, with the consequence that significant residual amounts of monomers and oligomers remain in the binder.
In aqueous dispersions or coating materials prepared from grafted binders, these monomer and oligomer residues lead to severe odor nuisance. It is readily evident that, following the application of such dispersions or coating materials, the monomers escape from the coating film together with the water, in the course of drying, and thus produce to an environmentally polluting emission.
Moreover, unsaturated monomers customarily used for the graft reaction, for example styrene or acrylates and/or methacrylates are hazardous substances with known toxicity. Thus, a need exists for an organic solvent-free, environmentally friendly, polybutadiene-based binder which is free of odor-causing residual monomers.
Accordingly, it is an object of the present invention to provide a completely solvent-free, environment-friendly polybutadiene-based binder without the disadvantages of the graft reaction, for example, the severe odor nuisance caused by residual monomers.
It is also an object of the present invention to provide a binder which exhibits rapid initial physical drying of the grafted binder.
It is, moreover, an object of the present invention to provide a binder having good coatings properties, for example outstanding corrosion protection integrity, good substrate adhesion, and sufficient stability on storage of the aqueous dispersions and pigmented systems produced therefrom.
The above objects and others are provided by a water-soluble or water-dispersible binder based on polybutadienes which is modified with at least 5% by weight of maleic anhydride or another ethylenically unsaturated dicarboxylic acid or an anhydride or a monoester thereof, and wherein at least 30% of the anhydride groups are present as imide groups from reaction with an amino carboxylic acid.
The present invention provides water-soluble or water-dispersible binders based on polybutadienes which have been modified with at least about 5% by weight of maleic anhydride and where at least about 30% of the anhydride groups have been reacted with amino carboxylic acids to form imide groups. In order to achieve good coating properties, in addition to rapid initial physical drying, from at least about 30 to 100%, preferably from about 45 to 85%, of the anhydride structures have been reacted with amino carboxylic acids, preferably with aromatic amino carboxylic acids, to form imide groups.
The remaining anhydride groups which have not been reacted will amino carboxylic acids can be reacted further, in whole or in part, with secondary amines and/or alcohols and/or aniline.
Aqueous dispersions or coating materials containing polybutadiene-based binders modified in accordance with the present invention no longer possess the disadvantages of odor nuisance as a result of containing toxic residual monomers, since graft reaction with unsaturated monomers is avoided.
In addition to rapid initial drying, further enhanced performance properties are also provided, such as compatibility of the binders with zinc-containing pigments, as well as good substrate adhesion and excellent corrosion resistance of the anti-corrosion paints produced from these binders. The storage stability both of the aqueous dispersions and of the pigmented systems prepared therefrom is, moreover, excellent.
Although DE-A 36 32 277 describes the reaction of maleic anhydride-modified polybutadienes with amino carboxylic acids; the binders described therein are, without exception, grafted with unsaturated monomers and therefore present the disadvantage of odor nuisance.
Further, DE-A 36 32 277 describes the reaction of grafted polybutadiene/maleic anhydride adducts with amino acids as improving the compatibility of the thus-modified binders with zinc-containing anti-corrosion pigments, so that the use of solvent can be avoided in the course of processing. Improved corrosion protection levels are also described. However, there is no mention of any improvement, or the feasibility of such, in initial physical drying.
One preferred embodiment of the invention entails water-soluble or water-dispersible binders based on polybutadiene/maleic anhydride adducts, containing:
A) from about 35 to 95% by weight of polybutadiene,
B) from about 0 to 40% by weight of hydrocarbon resins, and
C) from about 5 to 25% by weight of maleic anhydride,
wherein components A), B) and C) are chosen so that their sum is 100% by weight and the incorporated anhydride groups have been further reacted:
to the extent of from about 30 to 100% with aminocarboxylic acids
to the extent of from about 0 to 70% with secondary amines
to the extent of from about 0 to 70% with alcohols
to the extent of from about 0 to 70% with aniline
Preferred polybutadienes have molecular weights, determined as the numerical average, of from about 500 to 10,000 and iodine numbers, in accordance with Wijs of from about 300 to 500 mg of iodine/100 g of substance.
The preferred polybutadienes, moreover, preferably have molecular structures comprising from about 70 to 90% cis double bonds, from about 10 to 30% trans double bonds and from about 0 to 3% vinyl double bonds.
Mixtures of different polybutadienes and polybutadiene copolymers can also be employed.
Examples of hydrocarbon resins B. are described in: Karsten Lackrohstofftabellen, Curt R. Vincentz Verlag, Hannover 1992, 9th ed., p. 401 ff.; Encycl. Polym. Sci. Engn. 7, 758-782 Kirk-Othmer (3rd ed.) 12, 852-869, Ullmann (4th ed.) 12, 539-549.
These hydrocarbon resins are polymers of unsaturated compounds which are generally obtained from petroleum, coal tar or turpentine. Preferred hydrocarbon resins B) are unsaturated compounds which are able to react with maleic anhydride having a Cxe2x95x90C linkage with retention of the anhydride structure.
As component C), it is preferred for reasons of economy and reactivity to employ maleic anhydride. However, it is also possible to use other ethylenically unsaturated dicarboxyl compounds, such as ethylenically unsaturated dicarboxylic acids, their anhydrides or monoesters.
Examples of said compounds are maleic acid, fumaric acid, itaconic acid, 3,6-tetrahydrophthalic acid, itaconic anhydride, 1,2-dimethylmaleic anhydride, monomethyl or monoethyl maleate, for example.
The preparation of the polybutadiene/maleic anhydride adducts from A) polybutadienes, if used B) hydrocarbon resins and C) maleic anhydride takes place by known methods.
After adding a polymerization inhibitor, the components are heated generally for from 2 to 5 hours at temperatures from about 180 to 200xc2x0 C. under an inert gas atmosphere (nitrogen or argon, for example). The amount of the polymerization inhibitor generally lies within an order of magnitude of from 0.01 to 0.5% by weight based on the sum of A)+C) or A)+B)+C).
Examples of preferred inhibitors are hydroquinone, 2,5-di-tertbutylhydroquinone, hydroquinone monoethyl ether, copper naphthenate, copper acetylacetonate, phenylenediamine, and products based on alkyl and aralkyl-substituted phenols, for example.
The imidation reaction of amino carboxylic acids and, if used, aniline with the incorporated anhydride structures can take place by customary methods. It can be carried out in solution, but preferably in bulk, in the presence or absence of a polymerization inhibitor. The reactions take place at temperatures from 130 to 190xc2x0 C. and in reaction times of from 1 to 5 hours. The removal of the water of reaction formed can be accelerated by passing a stream of inert gas through the reaction mixture, or under reduced pressure.
For improving the initial physical drying, aromatic amino carboxylic acids are preferably suitable, examples being 2-aminobenzoic, 2-amino-4-chlorobenzoic, 2-amino-5-chlorobenzoic, 2-amino-6-chlorobenzoic, 2-amino-4-nitrobenzoic, 2-amino-5-nitrobenzoic, 3-aminobenzoic, 3-amino-5-nitrobenzoic, 3-amino-4-methylbenzoic, 4-aminobenzoic, 4-amino-2-nitrobenzoic acids, for example.
The use of aliphatic or cycloaliphatic amino carboxylic acids, for example, aminoacetic, 2-aminopropanoic, 3-aminopropanoic, aminobutanoic, aminohexanoic, aminooctanoic, aminoundecanoic, aminododecanoic, 1-aminocyclopentanoic or 1-aminocyclohexanoic acids, may lead to special and desired effects.
It is also possible to employ mixtures of different amino carboxylic acids.
The partial esterification with alcohols or imidation with secondary amines is effected by known methods.
The reaction can be carried out in solution, but preferably without a solvent, in the presence or absence of a polymerization inhibitor and/or of an esterification catalyst, at from 80 to 170xc2x0 C. Examples of preferred alcohols are methanol, ethanol, isopropanol, tert-butanol, ethylglycol, butylglycol, cyclohexanol, phenol, other modified phenols, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate or 2-hydroxyethyl methacrylate, for example.
Mixtures of alcohols can also be employed.
Examples of preferred secondary amines are dimethylamine, diethylamine, di-n-butylamine and dicyclohexylamine.
Mixtures of amines can also be employed.
For neutralizing the binders of the present invention it is possible to use inorganic bases, such as sodium or potassium hydroxide solution, for example. It is preferred, however, to employ ammonia and/or amines, examples being methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, dimethylaminoethanol, diethylaminoethanol, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol or morpholine.
Mixtures of amines can also be employed for the neutralization.
Neutralization of the acid functions of the present binders makes it possible to obtain aqueous dispersions having solids contents of up to about 50%. Degrees of neutralization of from about 0.7 to 0.95 are preferably established.
In the preparation of the aqueous dispersions a preferred procedure is to stir the resin melt into a hot mixture of deionized water and neutralizing agent which is at from about 50 to 90xc2x0 C.
The resulting aqueous dispersions have pH values of from about 7.0 to 10.0.
The dispersions can be used directly to produce clear films.
In general, however, they additionally contain pigments and further additives.
Examples of typical inorganic pigments are iron oxides, titanium dioxide, zinc oxide, strontium chromate and zinc phosphate. However, organic color pigments can be employed alternatively or additionally.
It is also possible to use customary additives such as, for example, driers, antioxidants, leveling assistants, stabilizers, antifoams, wetting agents, thixotropical auxiliaries and possibly fillers as well.
Preferred driers are the octoates, maleates, naphthenates, oleates and resinates of the metals cobalt, manganese, chromium, zirconium, iron, zinc, aluminum and calcium. Application of the coating materials, prepared from the present binders can take place by techniques customary in the art, such as spreading, spraying, dipping, pouring, rolling, etc.
Having described the present invention, reference will now be made to certain Examples which are provided solely for purposes of illustration and are not intended to be limitative.